Abstract:The fine soil filler contained in the subgrade of heavy haul railway will produce large deformation under the repeated action of train load, which will affect the safety of train operation. The train load is regarded as a continuous dynamic load in previous triaxial tests without considering the time intermittent effect. In order to investigate the accumulative plastic deformation and its dynamic and hydraulic characteristics of silty subgrade soil with different dynamic stress amplitude, water content, loading vibration times, intermittent time and relative coefficient (the ratio of intermittent time to loading time), drainage conditions, an intermittent cyclic loading dynamic triaxial test is carried out. Through the analysis of the test results, a method for determining the critical dynamic stress and critical moisture content of the soil by bilinear method is proposed, the critical dynamic stress ratio (the ratio of critical dynamic stress to confining pressure) changes linearly with the moisture content is found. It is found that the longer the loading interval time and the less the loading vibration times and the larger the relative coefficient, the smaller the accumulative deformation of the soil. And with the optimization of drainage conditions, the accumulative plastic deformation of the soil decreases in turn, the strength increases sequentially. The above research provides a theoretical reference for evaluation of hydrodynamic stability of heavy haul railway subgrade and rational selection of train interval time.

Abstract:The joint simulation method of Abaqus and Fortran to build the three -dimensional finite element analysis model of maglev train-track beam-subgrade-foundation coupling system based on the artificial boundaries condition for infinite element. The effects of different driving speed, subgrade stiffness and damping of subgrade bed on dynamic stress distribution and transmission law of low subgrade for medium and low speed maglev under medium speed driving are studied. The results show that the subgrade dynamic stress increases with the increase of running speed, and has little effect on the subgrade below 0.6 m; Under the condition of different subgrade bed stiffness, the greater the stiffness of subgrade bed, the greater the dynamic stress on the surface of subgrade, but the increasing amplitude is gradually slowing down, the dynamic stress of subgrade decreases with the increase of subgrade stiffness when the subgrade below 0.6 m; Different subgrade damping has no effect on the dynamic stress of the surface of subgrade, but it has a great influence on the dynamic stress at different depths under the subgrade, the larger the subgrade damping is, the smaller the dynamic stress of subgrade is, the greater the attenuation amplitude of dynamic stress is.

Abstract:Under complex environment and load, the deterioration of bridges resistance overtime will reduce the reliability and finally an unexpected failure occur suddenly impacting the durability, adaptability and safety of bridges. Therefore, it is of great significance to evaluate accurately the safety state of bridge and put forward timely reasonable suggestions and measures in maintenance, repair and resilience for bridge management and maintenance department. A Gamma stochastic process model for resistance degradation and a Poisson stochastic process model for live load were firstly established. Based on the two models and basic assumption that resistance and load effect are independent of each other, an expression for calculating structural failure probability was thus derived by using conditional probability formula, and an improved method to compute time-dependent probability calculation with Monte Carlo sampling was proposed. Finally, the Matlab language was used to compile the corresponding numerical program. As a benchmark example, the proposed method was used to investigate the attenuation law of reliability in resistance of a 20 years reinforced concrete T-beam bridge. Compared to the conventional method for calculating time-dependent probability , the present method not only is feasible and effective, but also has higher efficiency. In addition, taking the bridge resistance degradation model under corrosion mechanism as an example, The failure probability and reliability index of the bridge in the next 30 years are predicted.

Abstract:To quickly monitor and evaluate the prestress loss of Prestressed CFRP plate bridge in the early and late stage of reinforcement, a new distributed monitoring method is adopted to derive the long gauge strain numerical solution method of the concrete at the bottom of the beam after the end anchor is fully bonded with prestressed CFRP plate. On this basis, the prestress loss monitoring and evaluation indexes of static and dynamic prestressed CFRP plate are proposed; Then, through numerical examples, a three-dimensional numerical analysis model of multi piece small box girder strengthened with refined prestressed CFRP plate is established to study the influence of different vehicle parameters and different prestressed reinforcement levels on the accuracy of the static and dynamic prestress loss evaluation method. The results show that the error of static prestress loss evaluation method is less than 2.0%, and the error of dynamic prestress loss evaluation method is less than 2.8%, which proves the accuracy and theoretical feasibility of the proposed method.

Abstract:In order to study the road emission characteristics of national Ⅵ natural gas heavy-duty vehicle, the portable emission test system (PEMS) was used to carry out the actual road emission test of national Ⅵ natural gas heavy-duty semi-trailer tractor , and the relationship between pollutant emission factors and vehicle driving parameters was analyzed. The results show that due to the poor driving conditions in the urban area and frequent acceleration and deceleration, the two dynamic parameters are the highest. The driving conditions of the suburban expressway section are better, and the dynamic parameters are low.and the emission factors of CO, CO₂, NO_x and THC are the highest in the urban area and the lowest in the suburbs, which are positively correlated with the dynamic parameters. With the increase of vehicle speed, pollutant emissions gradually decreased, and the decline was relatively rapid at low and medium speeds. As the vehicle speed increased from 0~10 km/h to 10~20 km/h, and the emission factors of CO, CO₂, NO_x, and THC decreased by 25%, 69%, 43%, and 60% respectively; With the increase of acceleration, the pollutant emission gradually decreased, the emission factors are highest in the low-speed and high-acceleration range(v≤30 km/h, a≥0.8 m/s² ). It is recommended that the driver should avoid driving at low speed and high acceleration when driving this type of vehicle to reduce vehicle emissions. At the same time, the emission rates as well as the emission factors exhibited a strong positive correlation with the vehicle specific power (VSP). As a function of vehicle speed acceleration and road grade, VSP can quantify the emissions of China Ⅵ natural gas heavy vehicles, and thus model bus emission under the different driving conditions.

Abstract:The transportation sector is responsible for about 24% of global greenhouse gas emissions. Controlling the carbon emissions from the transportation sector is of great significance to achieve carbon neutrality. Based on analyzing the carbon emission process of various transportation modes, this paper analyzes the influencing factors of carbon emission factors of different transportation modes. Through the calculation model of carbon emission factors of different transportation modes, the size of carbon emission factors of various modes is analyzed. The research showed that the carbon emission factor of air transport is significantly higher than other modes of transport, followed by road, railway and water transport. Compared with the United States, the carbon emission factors of passenger transportation and freight transportation in China are all lower than those in the United States except air freight, China′s railway transport density is 4.4 times than that of the United States, and the carbon emission factor of freight and passenger transport is 50% and 81.56% of that of the United States.

Abstract:A probabilistic method for sector congestion prediction taking into account wind uncertainty is presented. Firstly, the ensemble trajectory prediction method subject to the uncertainty of wind forecast and the analysis method of the uncertainty of flight time prediction are studied. The ensemble trajectory prediction method based on weather ensemble forecasts is used to obtain the set of predicted trajectory. According to the trajectory set, the uncertainty of the look-ahead time is statistically analyzed, and the regression prediction equation of the flight elapsed time spread is established with the look-ahead time, sector entry point and flight time as explanatory variables. Then the sector probabilistic congestion prediction method is studied to obtain the traffic demand prediction set based on the trajectory prediction set and then calculate the sector congestion probability and the expected capacity missing value of the sector. The effectiveness of the proposed method is verified by using European Centre for Medium-Range Weather Forecasts (ECMWF) ensemble forecast data and historical flight plan data for typical busy sectors in China. The probabilistic congestion prediction based on the proposed method is beneficial to improve the effectiveness of Air Traffic Flow Management (ATFM) strategy and reduce the workload of controllers.

Abstract:In order to accurately explore the airport capacity utilization in China, airport capacity utilization index was proposed integrating "capacity demand" and "capacity supply", which evaluated the level of capacity utilization of 239 airports nationwide in 2019. Then, the capacity constrained airports were identified from the two dimensions of "full year" and "peak hour", the characteristics of which were explored in terms of spatial distribution, airport positioning, runway configuration and rush hour distribution. Finally, three future development scenarios were set to predict the capacity utilization of national and typical airports in 2025 and 2035. The research results indicate that about 92% of the airports in China are not capacity constrained, and there are significant differences among the airports. Eleven capacity constrained airports are mainly served as hubs and main coordinated airports. The airport capacity can generally meet the developing demand of civil aviation in China in the future, and only Shenzhen and Xi′an airports are expected to confront heavy capacity pressure. Combined measures can be taken from the two perspectives of "increasing capacity" and "balancing demand" to improve the matching degree of airport departure and landing demand with capacity supply, and to promote the level of airport capacity utilization.

Abstract:By establishing a three-dimensional coupled mathematical model, the effects of the current intensity and the depth of the electrode inserted into the slag pool on the temperature field and electromagnetic field during the electroslag remelting(ESR) process of G20 bearing steel were investigated. The magnetic field strength is mainly concentrated on the outer surface of the ingot. Due to the high electrical conductivity of the slag, the Joule heat of the system is mainly generated in the slag pool, and the highest temperature is located in the center of the slag layer. With the increase of current intensity, the current density of the whole system increases and the temperature increases. And with the electrode insertion depth increased from 10 mm to 30 mm, the temperature of the system showed a downward trend. At the current intensity of 1 500 A and the electrode insertion depth of 0.1 m, the maximum temperature of the central axis of the system is 2 187 ℃, and the average temperature of the slag-gold interface is about 1 600 ℃, which are all greater than the liquidus temperature of the steel ingot, which is 1 493 ℃. The molten molten steel passes through the slag layer and gradually solidifies to form an ingot, which can provide a theoretical reference for actual production.

Abstract:The velocity distribution in the molten pool has a significant impact on the cladding depth and width of the laser cladding layer and the surface morphology, which in turn affects the quality of the cladding layer. To this end, a thermal-fluid coupling model of laser cladding is constructed, and the cladding process under different laser power and powder feed rate is simulated by using it. Therefore, this paper uses this model to deeply study the effect of laser process parameters on the temperature field and the velocity field in the molten pool. It was found that as the laser power increases, the spot size or the scanning speed decreases, the peak value of the fluid flow velocity in the molten pool increases during the rising period, and the decline in the peak period of the flow velocity decreases gradually or even stabilizes. while the change of the powder feed rate has almost no effect on the velocity field. In addition, the influence of the surface tension coefficient on the velocity field in the molten pool is also studied.For the cladding material with negative surface tension coefficient, It was found that the fluid in the molten pool flows from the laser irradiation area to both sides, which makes the molten pool shallower and deeper.The cladding material containing active elements such as S has a positive surface tension coefficient, and the fluid in the molten pool flows from both sides of the molten pool to the middle, which makes the molten pool deeper and narrower. As the absolute value of the surface coefficient increases, the fluid velocity peaks will increase with it.

Abstract:A finite element model of self-piercing riveting of semi-tubular rivets was established by using the finite element software Deform-2D. The process of self-piercing riveted dissimilar metals of aluminum and steel was simulated and analyzed, and the stress distribution on rivets and metal sheets was analyzed. The self-piercing riveted tests and static tensile tests of AA5052 aluminum alloy and SPFC440 high strength steel dissimilar metals were carried out. The self-piercing riveted experiment of semi-tubular rivets for aluminum/steel dissimilar metals was performed. Tensile test and fatigue test were carried out to analyze mechanical properties of self-piercing riveted joint. The failure forms of the riveted joint are analyzed. The results show that the rivet head has good contact with the upper sheet, and the rivet shank spares evenly and smoothly in the lower sheet without crack or buckling. The stress of the rivet concentrates on the rivet shank, and the stress of the bottom sheet concentrates on the contact area between the rivet foot and the lower sheet. The results of numerical simulation and self -piercing riveted test are in good agreement. The relative error between simulation and test values is less than 13% , which meets the requirement of engineering design accuracy. The self-piercing riveted joint has good static tensile property and fatigue property. The maximum load of static tensile test is about 7.6 kN. The upper sheet warps and the rivet foot is pulled out from the lower sheet under the tensile load. The fatigue limit is about 2.3 kN under experimental conditions. In the process of fatigue loading, the aluminum alloy suffered fatigue failure under the combined action of fretting wear and tensile stress.

Abstract:The pore structure of air electrode has an important effect on the performance of lithium air battery. Therefore, based on the Comsol software platform, this paper developed a one-dimensional nonaqueous lithium air battery electrochemical model, and found that the simulation results by the present model are closer to the experimental results than those by the previously published model. What is more, the present model is widely used to investigate the effect of the air electrode porosity and its distribution, the particle size of porous carbon used to make the solid skeleton of air electrode, solid skeleton and pore phase tortuosity on the performance of lithium air batteries. The simulation results show that the air electrode porosity increasing, the discharge voltage platform and the capacity of nonaqueous lithium air battery increase. If the average porosity of the air electrode with the randomly porosity along the thickness direction is the same as the air electrode with the constant porosity, the discharge voltage platform and the capacity of the nonaqueous lithium air battery prepared by the air electrode with the randomly porosity are higher than the air electrode with the constant porosity. The results also show that the particle size of porous carbon decreasing, the discharge voltage platform of the nonaqueous lithium air battery increase, but the discharge capacity decrease. The solid skeleton and pore phase tortuosity increasing, the discharge platform and the capacity of nonaqueous lithium air battery decrease.

Abstract:In the field of electron backscatter diffraction (EBSD), Hough transform was introduced to realize the automatic identification of Kikuchi bands in EBSD patterns by means of computer, and EBSD technique has been developed into an important means to characterize orientation of crystalline materials. Since the speed of Hough transform is much slower than the moving speed of electron beam in scanning electron microscope, how to carry out Hough transform quickly has become a key problem that needs to be solved urgently in the whole EBSD field. In the present work, central processing unit (CPU) and compute unified device architecture (CUDA) were used to perform Hough transform on EBSD patterns, respectively, and the time consumption and recognition results were compared. The results show that the fastest recognition speed of Kikuchi bands is 1.7×10³ EBSD patterns per second for CPU. Under the same conditions, CUDA can process 1.7×10⁴ EBSD patterns per second, which is far faster than the fastest recognition speed of CPU. More importantly, Hough transform based on CUDA does not affect the identify results of Kikuchi bands in EBSD patterns. As a result, Hough transform based on CUDA technique will become a trend for fast identification of Kikuchi bands from EBSD patterns.

Abstract:In recent years, the integrity of railway scientific research has aroused concern from all walks of life. In order to analyze the integrity of railway scientific research in China, based on the Triple Helix Model and centered on the credibility of railway scientific research personnel, the cooperative relationship among universities, government and enterprises is expounded. This paper analyzes the status quo of scientific research integrity in China and the scientific research integrity in railway industry. From the aspects of system construction, moral construction and information management construction, this paper discusses the problems of the integrity of railway scientific research in China and puts forward some suggestions. The management of scientific research misconduct should start from system, education and big data technology, and build a governance model of "government, industry and learning".

Abstract:Based on the triple helix theory, this paper constructs a conceptual model of influencing factors of innovation performance of VR industrial cluster from the perspective of social network, uses structural equation method and data of relevant companies of VR industry in Nanchang to study the influencing factors of innovation performance of VR industrial cluster, and further studies the influence mechanism of R&D investment, government behavior and cluster atmosphere on innovation performance of VR industrial cluster.